Multicast only fast re-route for PIM ASM mode

Abstract

Techniques are described for enhancements to Protocol Independent Multicast (PIM) in an Any Source Multicast (ASM) mode in order to effectively implement Multicast only Fast Re-Route (MoFRR). According to the PIM ASM mode, a router operating as a last hop router connected to a receiver may initiate establishment of both a shared tree and a shortest path tree over which to receive multicast traffic for a given multicast group. According to the disclosed techniques, the router may use the shortest path tree as a primary path on which to receive the multicast traffic, and may use the shared tree as a secondary or backup path for MoFRR in case a failure occurs on the primary path. The techniques enable the router to perform MoFRR for PIM ASM mode without pruning the multicast traffic from the shared tree, and without building additional trees as secondary paths for MoFRR.

What is claimed is: 
     
       1. A method comprising:
 initiating, by a router in a network, establishment of a shared tree toward a rendezvous point (RP) router in the network using a first protocol independent multicast (PIM) join message that identifies a multicast group; 
 upon receiving multicast traffic for the multicast group over the shared tree, initiating, by the router, establishment of a shortest path tree toward a source of the multicast traffic for the multicast group using a second PIM join message that identifies the source and the multicast group; 
 upon receiving the multicast traffic for the multicast group over both the shared tree and the shortest path tree, defining the shortest path tree as a primary path and defining the shared tree as a secondary path for multicast only fast re-route (MoFRR); 
 programming, by a control unit of the router and into a forwarding unit of the router, a multicast route toward a receiver of the multicast traffic for the multicast group, the multicast route including the primary path and the secondary path; and 
 forwarding, by the forwarding unit of the router, the multicast traffic for the multicast group according to the programmed multicast route including forwarding the multicast traffic received over the primary path toward the receiver, and dropping the multicast traffic received over the secondary path. 
 
     
     
       2. The method of  claim 1 , wherein the shortest path tree and the shared tree are both active paths of the multicast group in the network. 
     
     
       3. The method of  claim 1 , wherein the shared tree and the shortest path tree comprise separate paths in the network that do not merge downstream from the source. 
     
     
       4. The method of  claim 1 , further comprising, upon detecting a failure in the primary path, performing MoFRR to switch from the primary path to the secondary path, wherein performing MoFRR comprises:
 updating, by the forwarding unit of the router, the multicast route for the multicast group; and 
 forwarding, by the forwarding unit of the router and according to the updated multicast route, the multicast traffic received over the secondary path toward the receiver. 
 
     
     
       5. The method of  claim 1 , further comprising:
 responsive to receiving the multicast traffic for the multicast group over the shared tree and initiating establishment of the shortest path tree toward the source, repressing, by the control unit of the router, establishment of another shortest path tree toward the source for MoFRR; and 
 responsive to receiving the multicast traffic for the multicast group over both the shared tree and the shortest path tree, repressing, by the control unit of the router, definition of another shortest path tree as the secondary path of the multicast route for MoFRR. 
 
     
     
       6. The method of  claim 1 , further comprising, responsive to receiving the multicast traffic for the multicast group over both the shared tree and the shortest path tree, repressing, by the control unit of the router, transmission of a PIM prune message that identifies the source and the multicast group on the shared tree, wherein transmission of the PIM prune message on the shared tree causes the multicast traffic for the multicast group to stop flowing over the shared tree. 
     
     
       7. The method of  claim 1 , wherein programming the multicast route comprises:
 selecting, by the control unit of the router, a first incoming interface (IIF) of the router for the shortest path tree to be a primary upstream interface for the multicast route; and 
 selecting, by the control unit of the router, a second IIF of the router for the shared tree to be a secondary upstream interface for the multicast route. 
 
     
     
       8. The method of  claim 7 , wherein forwarding the multicast traffic according to the programmed multicast route comprises:
 receiving, on a third IIF of the router, the multicast traffic for the multicast group; 
 comparing, by the forwarding unit of the router, the third IIF of the router on which the multicast traffic was received with the primary upstream interface for the multicast route; 
 based on the third IIF being the primary upstream interface, forwarding the multicast traffic received on the third IIF to the receiver; and 
 based on the third IIF not being the primary upstream interface, dropping the multicast traffic received on the third IIF. 
 
     
     
       9. A routing device comprising:
 a control unit configured to:
 initiate establishment of a shared tree toward a rendezvous point (RP) router using a first protocol independent multicast (PIM) join message that identifies a multicast group, 
 upon receiving multicast traffic for the multicast group over the shared tree, initiate establishment of a shortest path tree toward a source of the multicast traffic for the multicast group using a second PIM join message that identifies the source and the multicast group, and 
 upon receiving the multicast traffic for the multicast group over both the shared tree and the shortest path tree, define the shortest path tree as a primary path and define the shared tree as a secondary path for multicast only fast re-route (MoFRR), and 
 program, into a forwarding unit of the routing device, a multicast route toward a receiver of the multicast traffic for the multicast group, the multicast route including the primary path and the secondary path; and 
 
 a forwarding unit configured to forward the multicast traffic for the multicast group according to the programmed multicast route, wherein the forwarding unit is configured to forward the multicast traffic received over the primary path toward the receiver, and drop the multicast traffic received over the secondary path. 
 
     
     
       10. The routing device of  claim 9 , wherein the shortest path tree and the shared tree are both active paths of the multicast group. 
     
     
       11. The routing device of  claim 9 , wherein the shared tree and the shortest path tree comprise separate paths in the network that do not merge downstream from the source. 
     
     
       12. The routing device of  claim 9 , wherein the forwarding unit is configured to, upon detecting a failure in the primary path, perform MoFRR to switch from the primary path to the secondary path, wherein, to perform MoFRR, the forwarding unit is further configured to:
 update the multicast route for the multicast group; and 
 forward the multicast traffic received over the secondary path to the receiver according to the updated multicast route. 
 
     
     
       13. The routing device of  claim 9 , wherein the control unit is configured to:
 responsive to receiving the multicast traffic for the multicast group over the shared tree and initiating establishment of the shortest path tree toward the source, repress establishment of another shortest path tree toward the source for MoFRR; and 
 responsive to receiving the multicast traffic for the multicast group over both the shared tree and the shortest path tree, repress definition of another shortest path tree as the secondary path of the multicast route for MoFRR. 
 
     
     
       14. The routing device of  claim 9 , wherein the control unit is configured to, responsive to receiving the multicast traffic for the multicast group over both the shared tree and the shortest path tree, repress transmission of a PIM prune message that identifies the source and the multicast group on the shared tree, wherein transmission of the PIM prune message on the shared tree causes the multicast traffic for the multicast group to stop flowing over the shared tree. 
     
     
       15. The routing device of  claim 9 , wherein, to program the multicast route, the control unit is configured to:
 select a first incoming interface (IIF) of the routing device associated with the shortest path tree to be a primary upstream interface for the multicast route; and 
 select a second IIF of the routing device associated with the shared tree to be a secondary upstream interface for the multicast route. 
 
     
     
       16. The routing device of  claim 15 , wherein the forwarding unit is configured to, according to the programmed multicast route:
 receive the multicast traffic for the multicast group on a third IIF of the routing device; 
 compare the third IIF of the routing device on which the multicast traffic was received with the primary upstream interface for the multicast route; 
 based on the third IIF being the primary upstream interface, forward the multicast traffic received on the third IIF toward the receiver; and 
 based on the third IIF not being the primary upstream interface, drop the multicast traffic received on the third IIF. 
 
     
     
       17. A non-transitory computer-readable medium comprising instructions that when executed cause one or more programmable processors of a router to:
 initiate establishment of a shared tree toward a rendezvous point (RP) router using a first protocol independent multicast (PIM) join message that identifies a multicast group; 
 upon receiving multicast traffic for the multicast group over the shared tree, initiate establishment of a shortest path tree toward a source of the multicast traffic for the multicast group using a second PIM join message that identifies the source and the multicast group; 
 upon receiving the multicast traffic for the multicast group over both the shared tree and the shortest path tree, define the shortest path tree as a primary path and define the shared tree as a secondary path for multicast only fast re-route (MoFRR); 
 program, by a control unit of the router and into a forwarding unit of the router, a multicast route toward a receiver of the multicast traffic for the multicast group, the multicast route including the primary path and the secondary path; and 
 forward, by the forwarding unit of the router, the multicast traffic for the multicast group according to the programmed multicast route for the multicast group, wherein the instructions further cause the one or more programmable processors to forward the multicast traffic received over the primary path toward the receiver, and drop the multicast traffic received over the secondary path.